Spinal discs are the primary mechanical cushion for the vertebral column and permit controlled motion between the vertebral segments. Over time, these discs have a tendency to loose water which in turn reduces their cushioning ability. Along with a reduced hydraulic nature, the disc loses its ability to maintain disc height and bear loads resulting in a cascade of degenerative effects. As this degenerative process continues, a disc herniation involving bulging or expelling of disc material can occur leading to pain to the back and lower extremities. When this occurs, it is necessary to remove the herniated disc and reestablish disc height, ultimately in an effort to reduce or eliminate pain.
When the pain generating disc is removed, the disc space will collapse resulting in instability and further trauma to surrounding tissue and ensuing pain. Current treatments include installing a bone brace, cage, or other load bearing means often along with bone growth stimulators in an effort to cause fusion of the segment and thus alleviate the pain. This process is, however, believed to place undo stress on other vertebral levels as they compensate for the lack of motion, in turn potentially leading to premature failure of those other discs as well.
An improved solution includes replacing the removed internal portion of the disc, or the nucleus, with a nucleus prosthesis to act as the load bearing and motion stabilizing feature in an effort to restore natural spine biomechanics.
Devices such as these are outlined in U.S. Pat. No. 6,602,291 wherein the nucleus replacement is inserted into the disc space is a reduced size state, and then is hydrolyzed (or otherwise expanded) to fill the gap. Current methods and concepts have undergone human clinical trials to little success and suffers from an inability to access, place, and then finally secure the nucleus replacement in place. Several attempts at human trials have even resulted in expulsion of these devices out of the disc space. This problem must be addressed to make this technology a viable possibility in spine treatment.